The invention relates generally to metallurgical processes. More specifically, it is directed to coating processes for substrates such as turbine engine components.
A variety of specially-formulated coatings is often used to protect metal parts that are exposed to high temperatures, e.g., metal parts made from superalloys. For example, aluminide coatings are often used to improve the oxidation- and corrosion-resistance of superalloy materials. In aluminide coatings, the aluminum forms an aluminum oxide (alumina) film on its surface, which functions as a barrier to further oxidation. Such coatings may also serve as a bond coat between the superalloy substrate and a thermal barrier coating (TBC).
Several processes for depositing aluminide layers are available for both newly formed components and components under repair. Such processes include vapor phase deposition techniques and what is known in the art as the xe2x80x98pack cementation process.xe2x80x99 While vapor phase techniques are suitable for coating internal and external surfaces of a component, additional processing compexity may be an issue for certain applications. While the pack cementation process is effective at coating internal surfaces of a component, this process is expensive, time consuming, and requires highly specialized equipment, generally requiring the component to be shipped from the job site to an outside service provider in the case of components under repair.
Accordingly, a need exists in the art for further improved and alternative methods for forming aluminide coatings.
According to one aspect of the invention, a method for coating a surface of a substrate includes providing a substrate having a surface, and coating the surface with a foam suspension containing a powder suspended in a foam to form a coating on the surface. The substrate is then heat treated to densify the coating along the surface.